US2854662A - Pulse-echo system - Google Patents

Description

sept. 3o, .195s

D. H. wEsTwooD PULSE-ECHO SYSTEM 8 Sheets-Sheet 1 Filed Sept. 29, 1954 Dawn II. WESIWUDD Sept 30, i958 D. H. wEsTwooD 2,854,662

l `PuLsE-Ecx-xo SYSTEM Filed sept. 29, 1954 a sheets-sheet 2 mafie/imm if! fzzzgyff j WIr/winne INVENToR. Dax/IDH WESTWDQD Sep- 3G, i958 D. H. wEs'rwooD 2,854,662

PULSE-ECHO SYSTEM Filed sept. as. 1954 s sheets-sheet s .Dr-NID H. WESTWDQD Sept 30,1958 D. H. WEs-woon 2,854,662

PULSE-ECHO SYSTEM Arrow/5y wir Sept. 30, 1958 D, H, WESTWQOD 2,854,662

- l PULSE-ECHO SYSTEM l Filed Sept.l 29. 1954 8 Sheets-SheetI 5 -75 o 5 /0 /5 /0 Z530 55 4a 4f .fa

Ffm/

Sept 30 1958 v D. H. wEsTwooD 2,854,662

- PULSE-ECHO SYSTEM Fi 1ed fsept. 2e. 1954 a sheets-shea e 536 `INVENTOR. DHvm'I-I. WESTWUDD 1 Sept- 30,1958 D. H. WESTWOOD 2,854,662

PULSE-"ECHO SYSTEM Filed Sept. 29, 1954 8 Sheets-Sheet 8 9514/6. fol/555 i? I MMM/me man? fusi 75 A i fwn/www5 Fai fi, ao/ aa mmff 7j .574 f dam/Mrap# a; w Maz/*Mamme 66 [wise MM# /N/r/Hrio j/ l/ y wil/f rae/n .s/j ii/wf u rmi .5755/2 Mv/i Pas/mw Fae ,4L 7771/05 9501/7 73000/ 577 ini/m.:

J2! 6777's Foe/w50' EVB/fife- EN NAf/N6, ,4A/0 /NViem/: WA VE 3/9 (Pfiff/v7- ab' M005 of' wai ya) RAUM/fri? 7167665? 550 P/sf .m frio 5y @mf INVENToR'. Dawn H WEs-rwnnn r ff United States Patent O PULSE-ECHO SYSTEM David H. Westwood, Haddoneld, N. AI., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Arr Force Application September 29, 1954, Serial No. 459,146

29 Claims. (Cl. 343-13) The present invention relates to a pulse-echo (radar) system and in particular to a so-called direct reading, distance determining pulse-echo system.

A general object of the present invention is to provide an improved pulse-echo distance measuring system.

Another object of the invention is to provide an improved pulse-echo distance measuring system of the direct reading type, that is, of the type wherein a pointer or similar mechanical arrangement is used to indicate the distance to a reflecting object. l

Yet another object of the present invention is .to provide an accurate calibration circuit for the distance measuring system of the pulse-echo system.

A further object of the present invention is to provide a calibration system for a pulse-echo distance measuring system which enables the system rapidly to be calibrated at any and all ranges within the range of the system. v

Still another object of the present invention is to provide an improved pulse-echo distance measuring system which is light in weight and requires a minimum number of stages and circuit components.

Another object of the present invention is to provide an improved phase shifting circuit which is operative over an extended range.

It is another object of the present invention to provide a phase shifter of the above type which is extremely accurate over its entire range.

lt is another object of the present invention to provide a phase shifter of the above type having an inherent absolute accuracy which is substantially the same at maximum range as at minimum range.

A typical embodiment of the present invention includes a phase shifter. for accurately determining within predetermined angular limits the phase of a given wave with respect to a reference wave. Such a phase shifter may be, but is not limited to, a sawtooth phase shifter. The invention includes means responsive to the phase angle between the given and reference waves whenever the angle reaches either one of the above limits for shifting the phase of the reference wave by a known amount, not greater than the phase angle encompassed by the pair of limits, in the direction of said one limit. Thus, the comparatively limited phase shifting range between the two waves may be extended practically indefinitely in the direction of increasing or decreasing time referred to an arbitrary point on the reference wave.

A preferred form of the present invention comprises a pulse-echo system having a transmitter for transmitting a pulse to a reflecting object and a receiver for receiving the echo pulse reflected from the object. Means are provided for generating timing signals such as pulsesspaced from one another known intervals of time which are fractions of the time required for the transmitted pulse to reach an object at the extreme range of the pulse-echo system. The timing pulse generator may include a crystal controlled oscillator orother accurate time `basey oscil- 2 Y lator and means for deriving pulses of a given polarity f from the oscillator such as a sharpening, nonlinear ampli- Iier, squaring stage and differentiator or similar'circuit.,k

The main transmitted pulse is synchronized withy one of the timing pulses. The phase shifter, as above de scribed, is employed to generate a linear wave in phase: with a timing pulse which has a center region having a duration at least equal to the time interval between tim-v l ing pulses. The linear wave is so phased that the echo pulse occurs during the time of occurrence lof the center region thereof. .Y r f The linear wave extends through a reference voltage and means are provided for generating afsteep fronted wave coincidentally with the intersection in point vof time of the linear wave with the reference voltage. The phaseof a portion, preferably the center portion, of the steepr fronted wave is compared with that of the echo signal and a control voltage is derived having a sensedependent on the sense of the difference in phase between the two` signals. The control voltage is utilized to control a mechanical arrangement which adjusts the.A direct lvoltage level of the linear wave so as to bring thesteep frontedV wave into proper phase with the echo pulse while main.

taining the linear wave in its same phase relationship The mechanical 'arrangementl with the timing pulses. actuated by the control voltage is also utilized to actuate a direct reading device such as, in the case of a radi altimeter, adirect reading altitude indicator. y l. L

When the steep fronted wave, which follows the vphasei of the echo signal, is phase ,shifted to a point such that the intersection along the time axis of the reference voltage and the linear wave occurs at a point voutside vof the center region of the linear wave, control means are` actur ated for shifting the phase of the linear wave an intervaly equal to the interval `of time betweenadjacent timingI pulses. The shift is in the proper direction to return the point of intersection of the reference voltage andthe linearr wave to the center region of the linear wave but the in" tersection point along the time axis of the linear wave and the reference voltage is maintained the same by simule taneously shifting the direct voltagelevel oflthelinear: wave. Since the position of thesteep fronted wave' is dependent solely on the intersection along the time axis of the linear wave and the reference voltage.; its position remains substantially the same immediately lafteras im'- mediately before the shiftv ofthe 'lineariwave .-'lIhus,H the system providesl a continuous altitude indication throughout the range of thepulse-echo system.

In a preferred form of the invention the shifting of the linear wave by intervals equivalent to the' spacing between adjacent timing pulses is.control1ed by a-binary' divider chain, switches, relays, a geartra'in and a motor controlled by the control voltage. f Byfincreasingthe numbers of dividers, switches, and relays, the rangefof the equipment may be'Y extended indefinitely;-

The system also may include anovel calibration cir# cuit for accurately Calibrating it atfany altitude. This circuit comprises means for blocking the receiver during the reception of an echo pulse and rendering the trans: mitter operative coincidentally withone of the timing pulses which is closest in'point of time to the echopulse.'y

attenuated during the reception of the calibration pulse to prevent it from saturating.

The invention will be described in greater detail by reference to the following description taken in connection withthe accompanying drawings in which:

Fig. `l `is a block diagram of a typical embodiment of the invention; i Fig. 2 is a schematic circuit diagram of the gate circuit, pulse selectorcircuit, and calibration gate circuit shown in Fig. 1;

Fig. 3 is a schematic circuit diagram of the fast (steep wave) and slow (linear wave) sweep circuits and clamper circuits shown in Fig. l;`

Fig.KV 4 is a block and schematic circuit diagram of the phase detector shown in Fig. l;

Fig. 5 is a schematic circuit diagram of the motor control system shown in Fig. l;

Fig. 6,is-a schematic circuit `diagram of the timing pedestal circuits of Fig. 1;

p Fig. 7 is a chart showing the phasing of various relays and certain circuit elements contacted thereby shown in Figs. l, 2, 3 and 6;

l Fig. 8 is a diagram of various waveforms present in the circuit of the present invention;

Fig. 9 is a diagram illustrating the phasing under certain conditions of the steep fronted and linear fronted waves; 4

Fig. 10 is a schematic circuit diagram of the calibration system of the present invention; and

Fig. 1l is a diagram of various waveforms present at different points in the calibration circuit.

f Through-out the figures similar reference numerals refer to similar elements.

SYSTEM OPERATION .The present invention is particularly applicable to the measurement of altitude, that is, the elapsed time between the transmission of a radar pulse and the reception of a ground echo. It is to be understood, however, that the system is applicable to any type of radar system wherein it is' desired to` determine the distance t-o a reflecting object. Also, it is equally applicable to any system wherein it is desired to determine the time delay between a reference pulse and a variable time delayed pulse which is synchronized with the reference pulse and occurs `atfsome time interval following the reference pulse. i

w In` a preferred form of the invention a difference in timing between a received echo pulse and a predetermined portion ofa steep fronted wave causes a voltage of proper polarity to `be applied to the servomechanism to correct the phase position of thelatter with respect to the former.,` ,In so doing, the indicator, which may comprise a dial with altitude digits and an indicator pointer, is set to` the correct altitude indication.

Some ofthe rmore important circuits in the system are shown in the block diagram` of Fig. l. Circuits such as those for blanking the receiver and adjusting the gain thereof, conventional receiver indicator circuits, other detailed circuits lof the receiver and transmitter and other conventional circuits which play no part in the present invention are not discussed in detail.

Referring now to Fig. 1, timingfor the system is established by a ystable `98.329 kc.` oscillator 20 (hereinafter identified as 98 kc. for purposes of simplicity) the output of which has a period between voltage peaks equal to thelradar pulse transit time for 5,000 feet of altitude. The `output of the oscillator is applied through phase shifter 22, the purpose of which will be explained later, to a chainof` five binary dividers 24, 26, 28, 30 and 32, respectively. The dividers may comprise ve cascaded bistablemultivibrators each having a pair of output anodes- A, B and successive multivibrators providing output waves having twice theperiod of the preceding multivibrator. rl`he respective outputs at plates A and B of each multi- 4 vibrator are 180 out of phase as shown in Figs. 8cl, inclusive.

Two separate outputs are obtained from the divider chain; the rst from lead 34 supplies the trigger channel and the second from lead 36 supplies the timing channel. The two mixed `outputs occur at a rate of 3.073 kc. (hereinafter identified as 3 kc. for simplicity).

The output of loscillator 20 is also applied to ringing amplifiery 48, ringing amplifier and cathode follower 52. These three stages derive from the sinusoidal wave a plurality of pulses as shown in Fig. 8b having a recurrence rate of 98 kc., which it will be remembered is equivalent to 5,000 feet of radar altitude. The stepped waveform output taken from lead 34 and shown in Fig. 8m is applied to gate circuit 54 the output of which is Aapplied to pulse selector 56. As will be explained more fully below, when the most positive going portion of the trigger pedestal corresponds with one of the output pulses from cathode follower 52, pulse selector 56 is rendered conductive and applies an output signal to blocking oscillator 58. The latter triggers transmitter 60 causing it to transmit an output pulse.

In the description above, ringing amplifiers are employed'to derive pulses from a sinusoidal wave. It should be understood that the invention is not limited to this specific pulse forming means as others such as squaring limiters, blocking oscillators, multivibrators or the like, as will be apparent to thoseskilled in the art, may be used instead.` Moreover, other pulse yforming means could be substituted for blocking oscillator S8. Finally, gate producing means other than bistable multivibrators may be employed for the binary divider chain 24-32.

Relays 38,. ,40, 42, and 44 which are individually actuated by relay actuator `:means 46 determine which outputs of divider stages 24, 26, 28 and 30 will be connected to `lead 36. The relay actuator means 46 therefore determines the phase of the timing pedestal Ishown in Fig. 8o.

The timing pedestal is supplied to gate circuit 62 which is'substantially identical t-o gate circuit 54. The pulses from cathode follower 52` are supplied to pulse selector 64 which is substantially identical` to pulse selector 56. Whenthe most positive going portion of the timing pedestal is in coincidence with one of the output pulses of cathode follower 52, pulse selector 64 is rendered con ductive `and supplies a triggering pulse to multivibrator 66. Multivibrator 66 actuates linear wave generator 68 which in turn actuates steep Wave generator 70. The

phasing of the linear and steep waves is shown in Fig. 8, waveforms q and r.

Clampe'r` 72, potentiometer 74 and reference voltage source 7S determine the phase position of the steep fronted wave, as will be explained more fully below, and

phase, no outputsignal is applied to the following stages.v

In phase is defined as that `condition in which the echo pulse coincides with `the ground cross-over point of the steep wave.` Ijtthe two signals are out of phase, a signal having a polarity dependent upon the sense of the out of phase condition is applied through resistor-condenser network 82, motor control S4 andmotor 86 to gear train 88. `The gears rotate the arms of potentiometer 74 via` mechanical connection 89 and drive the steep fronted wave into phase with theecho pulse.

At `the same time gear train 88 actuates altitude indcator90 and altitude deviation indicator 92 to provide a true reading of altitude and an indication of any deviagestisce tion in altitude from a predetermined or present altitude, respectively. Gear train 88 also controls relay actuator means 46 through cams 94, switches 96 and mechanical connection 97 in a manner which will lbe explained in The function of phase shifter 22, Fig. 1, is to properly phase the trigger and timing pedestal waveforms with respect to the 98 kc. pulses so that the latter fall near the center of the most positive going portion of the refurther detail later. spective pedestals. The phasing of the pedestal waves is Calibration gate circuit 98 (lower left comer of figure) not critical but operation is most stable when the 98 kc. 'l connected to the output of multivibrator 66 provides a pulses Occur near the center of the most positive going calibration signal for the system which enables the sysportion ofthe pedestal, as already indicated. tem to be accurately calibrated at any aircraft altitude. Referring 110W t0 the table ahOVe, Combination 2 WaS This signal is normally shorted to ground through the cir- Selected hy PefmaheDt'COIlheetiOIlS t0 fOllTl the trigger cuit including relay contact 100a and condenser 101. pedestal. It can be shown that combination 3 will pro- However, when the calibration switch (not shown in Fig. duce a Wave having its high step immediately adjacent l) is closed and relay 100 actuated a calibration pedestal and following that 0f Combination 2 and that Succeeding gate is applied to gate circuit 54. This circuit will be COmhiietOIlS form Pedestal WaVeS With their highest explained in more detail below. steBps folllowing1 in Seqlleheel 38 40 42 d 44 d y se ective y operating re ays an an BINARY DIVIDER CHAIN employing the resultant pedestal wave for gating, it is Since the bistable multivibrator circuits making up'the possible to pass successive ones of the first 16 pulses debinary divider chain 24, 26, 28, 30, and 32 are convenrived from the 98 kc. oscillator to the timing channel. tional, they are not illustrated in detail. VFor the trigger Each succeeding pulse provides a time delay equal to channel fixed taps on the divider outputs provide a ped- 5,000 ft. in radar range. estal waveform occurring at a 3 kc. repetition rate. As The relays 38, 40, 42 and 44 are so energized that can be readily shown from a consideration of waveforms combination 1 forms the timing pedestal when the indic-l of Fig. 8, the most positive going portion 102 of cated altitude is between zero and 2500 ft.; combination waveform m occurs in the phase position indicated, This 2 is used `between 2500 ft. and 7500 ft.; combination 3 is trigger pedestal gate causes the selection of pulse 103 used between 7500 ft. and 12500 ft., et cetera. This will (Fig. 8) which triggers the transmitter 60. Pulse 103 be explained in further detail in connection with Fig. 7. therefore occurs at a time equal to zero altitude.

For the timing channels, the divider outputs are mixed GATE CIRCUIT 54 AND PULSE SELECTOR 56 in a predetermined manner as determined by relay actu- Figure 2 includes `a circuit diagram of the gate circuit ator means 46 and relays 38, 40, 42 and 44 to develop 54 and pulse selector 56. These circuits provide the triga timing pedestal gate pulse at a 3 kc. pulse repetition ger pulse for the transmitter 60 by selecting every 32nd rate. There are 5 multivibrator stages and therefore 25 pulse derived from the 98 kc. oscillator. Sharp, low imor 32 different possible combinations of divider stage out- 35 pedance pulses from cathode follower 52 are applied to puts. Since, however, there is no choice provided for the the control grid 132 of triode 134. Triode 134 is norffth divider l32, only 16 combinations are available. As mally biased to cutoff by the potential applied to its catha matter of fact, in a form of the invention actually built, ode through resistor 142, and the negative bias developed only 13 of the combinationswere required since these 13 across grid bias capacitor 144. provided 4altitude indications up to 60,000 feet. In this 40 Gate circuit 54 comprises triodes 136 and 138. The form of the invention the use of combinations 14, 15 and control grid 146 of triode 138 is maintained at a con- 16 was prevented by mechanical stops. stant positive pontential by a voltage applied thereto It is to be understood that in embodiments of the infrom voltage divider 148, 150. Thus, triode 138 norvention where distance measurements of greater than mally conducts and its plate voltage which is applied to 60,000 or 80,000 feet are of interest, these may readily the control grid 132 is maintained at a low value. be obtained by using the entire divider chain, adding ad- The trigger pedestal gate output of the chain of binary ditional divider chains and relays, or using an oscillator dividers is applied to the control grid 152 of triode 136. as the time base of the system which has a frequency Cathode 153 follows the voltage waveform of the trigger lower than 98 kc. For example, if a 98 kc. oscillator is pedestal gate and when the maximum positive step of employed and there are 10 divider stages each having two 50 the pedestal wave occurs, the cathode 154 of triode 138 possible outputs, there will be obtained 21D yor 1024 posis driven suiiciently positive to decrease the current sible combinations of divider stage outputs which is through triode 138. This causes an increase in the anode equivalent to (21X5,000 ft.) or about 1000 miles. voltage of triode 138 which in turn drives control grid In the form -of the invention illustrated, the 16 pos- 132 sufliciently positive to allow one coinciding 98 kc. sible combinations of outputs available are as follows: pulse to render triode 134 conductive. Since the mo'st Table I Combination No. Divider BABABABABABABAB ABBAABBAABBAABB AAABBBBAAAABBBB AAAAAAABBBBBBBB` AAAAAAAAAAAAAAA' lt will be apparent that combination 2 is the one propositive going portion of the pedestal Wave occurs at a vided by the fixed contacts for producing the trigger ped- 3 kc. rate, there is provided an output pulse Sn which 's estal pulse. Waveform o of Figure 8 (combination 5) supplied to blocking oscillator 55 coincident with every represents the output of plates A of the first and second 32nd input pulse 8b. dividers, plate B of the third divider and plates A of the The calibration circuit including multivibrator 66, fourth and fifth dividers. The peak-of this pedestal is calibration gate circuit 98, relay 100 and calibration shown at 102er. The pulse 104 of waveform p, Fig. 8, switch 155 will be explained in further detail below. selected by waveform o occurs 15,000 ft. after the trans- As previously mentioned, pulse selector 64 and gate mitted pulse.

circuit 62 in the timing channel are substantially identical of the multivibrator plate.

with the analogous components gate circuit 54 and. pulse selector 5.6 in the trigger channel and therefore the former will not be discussed in detail.y f Suffice it to say that the every 32nd y98 kc. pulse, the one selected depending upon the positions of relays '38, 40, 42, and. 44, which in turn depend upon the altitude of the aircraft.

LINEAR rWAVE GENERATOR 68 nection of triode 178 to the cathode of triode 176 im@ proves the cathode follower action.

' pulse selector and gate Acircuit inl the timing channel select In operation, during the positive half of squarewavel y y170, diodes. l172 and 174 conduct. The capacitor net- l work 180, 182 andte'mpe'rature compensating capacitors 184, 186 charge through diodevl'lZtothefullvoltage The voltage appearing across resistor network '10d' is equal lto the voltage of the multivibratorplate neglecting the sniall'voltage .dropsacross during this period is positive as indicated by waveform Sq. At the termination of the positivey half. cycle of the multivibrator input, the input suddenly goes negative andv diode 172 is cut on". yThe capacitor network which is charged to its highest potential begins discharging through l resistor network 188 and diode 174. The grid and cathode of triode 176 thereby go negative.l The negative cathode voltage change of 'diode-176 is 'applied through. capacitor 190 tothe plate of diode 17e and cuts the latter off.

The` discharge path yof' the rcapacitor network -is now' through the resistor network and intol the negative side of capacitor 190. Since the` voltage at both ends'of resistor network 188 change at practically the same rate,

the current throughthe resistor is substantially constant tion' is at the-instant one of relaysf, d0, i2 orali cause y a new timing pedestal to be' selected, andoccurs-at 2500 diodes 17.2 and 174. The output taken from lead 192 207 or 208,-whichever'onel is in circuit).y As will be .ex-

plained more fully below, arms'207','208 .are incircuit and the capacitor network discharges at substantially a' linear rate. The voutput at lead 192 then also falls at a linear rate Aafterv diode 172 is cut ot. The slope of the linear output wave may be adjusted by varying the position of potentiometer arm 194.

The action described above results in an output wave that is slightly non-linear because the grid-to-cathode voltage of a tube is not constant for different plate currents and plate-to-cathode voltages. To compensate for this effect, the grid voltage of triode 176 is made non-linear in such a way as to make its cathode or output voltage linear. This is accomplished by resistor 19" secured between the cathode of triodc 176 and the mid-point of the capacitor network.

The linear portion of the linear wave is approximately equal to two 98 kc. pulse intervals or 10,000 ft. of radar range. The linear wave is moved in 5,000 ft. steps as the indicator changes indicated altitude. Interpolation between pulses is by means of a steep wave to be discussed next.

STEEP WAVE GENERATOR 70 will be described in more detail below, determines which one of the arms is in circuit. The bias voltage applied to control grid 202 of triode 204 is determined by the position of arm 209 along voltage divider 210, 211, 212. In practice, arm 209 is set during the calibration of the instrument and remains in its set position.

Arms 207 "8 and 208,011 the lother hand, change their position as thefaltitudey of the aircraft changes.

In operation, the steep wave generator'is essentiallyv a comparison amplier. When the potential on grid 198 .is more positive than the potential on grid 202, pentode y 200 conducts and triode 204 is cut orf. This'is `because the flow of ycurrent through pentode 200 and common cathode resistor 205 makes the cathode 213 positive withy y Under this .condition the respect to control grid 202. output voltage at the anode 214 is maximum and equal to the B+ voltage.v Arm 20? which furnishes the bias to, grid 202, hereinafter referred to as the reference voltage,

determines the voltage to which the cathode 213 must be vlovveredin order to render triode 204 conductive.

During the negative going portion of theflinear wave, cathode follower action of pentode 200 causes the voltageacross cathode resistor 20S alsoy to lgo more negative and nally a point is reached on' the negative slope of wave 82 at which rthe cathode-to-grid voltage of tube 204 is such as -to render. thev tube conductive. As a result, the

anode voltage of the tube rapidly ldrops producing the steep wave fronty 31'.l y l .Summarizing, when voltage on grid 19S is more positivel than the reference voltage, the' plate voltage lof 204 is high; and when ythe voltage on grid 198 is more negative vthan thereference voltage the plate voltage of 2,04 is ,y low, the transition between high and low points providing y l the steepl fronted wave. it is seen then that the position -of the steep wave alongl the time base is dependent on the reference voltage (the position of arm r209). and. .l

on the D. C. level lo1? the linear wave (the position of arm successively vfor successive 5,000. toot ranges. The transift. andodd multiples thereof.

the output of which is clamped by clamper '77 -to .a potential suchthatthe center of the steep wave is always at ground potential.

The manner of operation of the linear and steep wave generators and related circuits will more clearly be understood by reference to Fig. 9. Assume that the aircraft is at zero altitude. In such case, assume that the clamping voltage is Vc and that the reference voltage is Vr. As already mentioned, the linear waveform encompasses a range of approximately 10,000 ft., extending in the present case from 5,000 ft. to |-5,000 ft. Steep wave r' `is initiated at the instant the linear wave becomes more negative than the reference voltage Vr as indicated by dashed line 215. As the aircraft increases its altitude the phase between a ground echo and the steep fronted wave changes, and, as will be explained in more detail later, a voltage is developed by the phase detector (Fig. l) and fed through network 82 and motor control 84 to motor 86. Motor 86 in turn causes gear train 88 to move potentiometer arm 207 (shown in Fig. 3 as being in circuit) in the correct direction to increase the clamping voltage applied to control grid 198. During this interval the reference voltage Vr which, it will be remembered, has been preset during calibration of the equipment, remains constant. Moreover, during this interval the phase position of the linear wave with respect to the 98 kc. pulses remains the same. The result is that as the aircraft altitude changes the point of intersection along the time axis of the reference voltage Vr and the linear wave also changes.

After the aircraft has reached an altitude of about 2500 ft. the clamping voltage has reached a new value Vc-t-x and the steep wave has moved along the time or altitude axis from its original position r to a new position r" with respect to the still stationary position (with respect to time) of the linear wave q. ln other words, if the altitude of the aircraft increases up to a certain altitude, the phase position of the linear wave remains the same and the phase angle between the linear wave of the steep wave increases.

When the aircraft reaches an altitude of about 2500 ft. relay 130 (Figs. 3, 6 and 7) is actuated. Two actions result: Potentiometer arm 207 is removed from the clamping circuit and potentiometer arm 208 is placed in the circuit (Figs. 3 and 6), and relay 38 (Fig. 6) is actuated causing plate B of divider 1 to be placed in the timing pedestal circuit. The first action causes the clamping voltage level to assume a new level Vc-x and the second action causes a 5,000 ft. shift in the point at which the linear wave is initiated, as shown in waveform q", Fig. 9. As can be seen from waveform q", the combined effect of changing the clamping voltage level back to level Vc-x and shifting the linear Wave an amount equivalent to 5,000 ft. is that the point of intersection of the reference voltage V1r and the linear wave remains precisely the same. Thus, the phase position of the steep wave immediately after transition relay 130 is operated is precisely the same as immediately before it is operated as shown by wave r", Fig. 9. p

The above action enables the steep wave to be smoothly moved from a position corresponding to zero aircraft altitude through the entire range represented by the combinations in Table I above. In each case, it is possible to move the steep wave through an increment equal to about 5,000 ft. after the time the linear wave is transposed to a new position. It is then possible again smoothly to move the steep wave through 5,000 more feet after which the linear wave is again transposed 5,000 ft., etc. The transpositions occur at +2,500 ft., i-7,500 ft., etc. as shown in Fig. 7.

It will be observed that the precise time at which each relay 38, 40, 42 and 44 is operated need not be extremely accurate. Also, it should be noted that it is not possible for the dividers and switching circuits to lose count since the trigger pedestal wave m (Fig. 8) bears a relationship to the timing pedestal wave o (Fig. 8) depending upon the status of the four divider relays. If the circuit is turned on when the delayed pulse is occurring somewhat removed from the balance point of a steep fronted wave, an error voltage remains until the servo proceeds through all switching sequences necessary to bring the linear and steep waves into proper phase with the received echo pulse.

PHASE DETECTOR 80 The phase detector employed in the present circuit is substantially identical with the one illustrated in Fig. 4 of application Serial No. 177,486, jointly filed August 3, 1950, by Robert Trachtenberg and the present applicant and now issued as Patent No. 2,713,160, dated July 12, 1955. The circuit functions to compare the timing of the steep wave and a received echo pulse. When the echo pulse is in phase with the steep wave, that is, when it occurs -coincidentally with the center portion of the steep Wave as illustrated in Fig. 8, waveforms r and s, there is no output from the phase detector. Any difference in timing, however, between the steep wave center and the echo pulse, which signifies a difference between the absolute altitude of the aircraft and the altitude indicated on the altitude indicator 90 (Fig. l), will result in the development of a voltage of the proper sense to cause motor 86 to drive the altitude indicator and simultaneously correct the phasing of the steep Wave and echo pulse.

The circuit is shown in Fig. 4 and includes four diodes 220, 222, 224- and 226. The steep wave 8f which is clamped at one end by clamper 77 to a voltage such that its center is at ground potential is applied to point 228 so that this point goes both positive and negative with respect to ground. The echo pulse is applied to the primary winding 229 o-f transformer 230 and is stepped up in amplitude. The center tap of secondary winding 231 is grounded and the secondary polarities are such that positive pulses are applied tothe anodes of diodes 220 and 224 and negative pulses are applied to the cathodes lof diodes 222 and 226. Diode conduction during the pulses charges capacitors 232 and 234 to almost the peak pulse amplitudes. This charge establishes a bias on the diodes which holds them far below cutoff for the entire time between pulses. During the top portion of the echo pulse, however, the diodes are driven into conduction and points 228 and 236 are electively connected together through the conducting diodes. Point 236 then assumes whatever voltage the steep wave may have at the instant the echo pulse arrives. It is clear then that if the echo pulse is properly centered on the steep wave front there is no voltage to ground developed across capacitor 238. If the echo pulse is not properly centered on the steep waveform there is a voltage developed with respect to ground having a sense dependent on the phas- 4ing of the echo pulse and steep waveform. Any voltage developed at point 236 is smoothed out and retained between pulses by the R-C network comprising capacitor 238, resistor 240`and capacitor 242.

The result of the operation described above is that any difference between indicated altitude and absolute altitude also provides a difference in phasing between a received echo pulse and the steep fronted wave. This dif- Iference causes a voltage output of the phase detector which when amplified in the motor control circuit drives the indicator in the correct direction to reduce the altitude error to zero.

MOTOR CONTROL CIRCUIT 84 It will be apparent that numerous types of motor control circuits known in the art may be employed between the phase detector and reversible motor 86. For example, the motor control circuit shown in Fig. 5 of application Serial No. 177,486, mentioned above, may be employed.

A preferred embodiment of the invention includes the phase detector of Fig. 5. This -circuit is essentially a direct current amplifier and consists of three sets of triodes 250, 252; 254, 256; and 25S, 260. The phase detector output is fed to grid 262 of direct current differential amplifier 250, 252 and to grid 264 of cathode coupled rate amplifier 258, 260. The presence of a direct current signal on grid 262 gives rise to an unbalanced or push-pull output at plates 266, 268. This output is D. C. coupled to grids 270 and 272, respectively, and causes an unbalanced current in the two tridoes 254, 256. The plate currents of triodes 254, 256 are applied to different halves of field winding 274 of motor 86. As can readily be seen, when there is more current owing through one half of the held winding than the other, the mo-tor will run in a direction determined by the stronger of the two fields. The direction of rotation of the motor is in the proper sense to reduce the altitude error to zero and simultaneously to correct the phase position of the steep wave and received echo signal.

The output of the rate amplifier 258, 260 is capacitively coupled to grid 276 of triode 252. Triode 252 amplies the alternating current rate components of the error voltage to provide damping for the servo loop. Capacitor 278 by-passes a substantial portion of any noise signal which may be present but the rate information is not changed to any substantialdegree below its input level.

TIMING PEDESTAL CIRCUITS As previously explained, the timing channel requires successive 98 kc. pulses (5,000 ft. spacing) as the aircraft travels through successive 5,000 ft. ranges. These pulses are selected by the timing pedestal formed by the chain of binary dividers, the selection being controlled by relays 38, 40, 42 and 44. Thus, different 5,000 ft. altitude ranges cause different pulses (104, Fig. 8) to be selected to initiate different linear sweeps extending through the particular setting of the altitude indicator. The circuits for accomplishing the above are shown in Fig. 6 and the phasing of the various elements of the circuit in Fig. 6 is shown in Fig. 7. The circuit includes four cams 290, 292, 294 and 296. In one form'of the invention the cams may rotate at the same speed, cam 290 being provided with 221t cut-out sections, cam 292 with 45 cut-out sections, cam 294 with 90 cut-out sections and cam 296 with a 180 cut-out section. The gearing S8 is so adjusted in this form of invention that cams 290, 292, 294 and 296 malte one revolution in 80,000 ft. The arms 207, 208 of linear potentiometer 206 make one complete revolution each 10,000 ft. of altitude.

In a second form of the invention the gearing 88 may be so adjusted that cam 290 has less than 8 teeth provided it operated at a higher speed than the other cams. ln a model of the invention actually constructed cam 290 did in fact comprise a single rather than a multiple cam and operated at a higher speed than the remaining cams.

The switching action can be best understood by referring to Figs. 6 and 7 at the same time. Assume that the circuit is initially at zero altitude and that the aircraft is climbing. From the previous discussion and by referring to Table I it is seen that at zero altitude the relays 38, 40, 42 and 44 should select the A plates of each divider. Figure 6 shows this condition, each of the relays being unenergized. As the aircraft increases its altitude, the phase position of the echo pulse with respect to the steep waveform tends to change resulting in an output direct current signal of the proper sense to start motor 86 operating. The motor rotates the cams through the gearing 88. At an altitude of about 2500 ft. tooth 298 of cam 290 bears against the arm of switch 300 and closes the switch. This completes the circuit of relay 130 and relay contacts 130-1 to 130-10 are all thrown from their even numbered to their odd numbered positions. This completes the circuit of relay 3i; which places plate B of divider 1 in circuit. Referring again to Table I, it is seen that the combination BAAAA is combination 2. Relays 40, 42 and 44 are not energized because their ground returns are open at cams 292, 294 and 296, respectively. However, actuation of relay 130 does cause the selection of the second arm of linear potentiometer 206 which changes the linear wave clamping level in the manner previously described.

When the aircraft attains an altitude of about 5,000 ft. the cams have moved about 45 and cam tooth 302 of cam 292 engages brush 304. This, however, does not complete the circuit of relay 40 since arm 306 is engaged with Contact 130-3.

As the aircraft continues to gain altitude and reaches about 7500 ft., cam tooth 298 becomes disengaged from the arm of contact 300 and relay 130 opens. The release of relay 130 causes the return of contact arm 30S to contact position 130-2 releasing relay 38 and returning divider 1 to the A multivibrator plate. the release of relay 130 causes arm 306 to move to contact 130-4 which, it will be remembered, is now grounded through tooth 302 of cam 292. Thus, relay 40 is energized and plate B of divider 2 is selected. Relays 42 and 44 remain unenergized. Referring again to Table I, combination ABAAA is the third combination. The release of relay 130 also causes transposition to the arm of linear potentiometer 206.

f the above operation is carried out for the entire range of the radio altimeter it will be seen that the combinations of Table l are successively set up. Each cornbination will be set up at the precise time that relay 130 transposes at odd multiples of 2500 ft.

CALIBRATION CIRCUIT The calibration circuit permits fixed error to be calibrated out of the equipment while the aircraft is at any altitude, the calibration point being zero or the 5,000 ft., setting which is nearest to the aircraft altitude. The

At the same time,

circuits involved are shown in Figures 2 and 10 and pertinent waveforms in Fig. 11.

Referring now to Figs. 2 and 10, calibration switch 155 is of the type which may be rotated when closed. It is mechanically connected through connection 312 to arm 209 of voltage divider 210, 211, 212 (see also Fig. 3) and, when rotated, adjusts the position of arm 209. Arm 209 controls the reference voltage applied to control grid 202 of triode 204.

When the calibration switch is closed, relays and 310 are actuated. Their function is described below.

For purposes of explanation, assume that the conditions of the equipment are as shown in Fig. 11, waveforms S12-319, respectively. The aircraft is at an altitude of approximately 17,000 ft. The transmitter pulse occurs at zero altitude as shown in waveform 313. The timing pulse for the 12,500 to 17,500 ft. range occurs at a time equivalent to 10,000 ft. of altitude as shown in waveform 314. Output Wave 315 at plate B of multivibrator 66 initiates linear waveform 316. The steep wave position occurs at a point in time corresponding to the intersection of the reference voltage and the linear waveform as shown by curve 317. The echo pulse 318 occurs at an altitude of approximately 17,000 ft.

When relay 100 is energized the short-circuit is removed from contact 100a and applied to contact 100b (Figs. 2 and 10). This shorts the trigger pedestal gate which is normally applied to the control grid of triode 136 in gate circuit 54.

Referring to Figs. 2, 10 and 11, the positive output 319 at plate A of multivibrator 66 is differentiated by ditferentiating network including capacitors 320 and 322 and resistor 324. The peak portion of the differentiated wave is amplified by triode 326 of the calibration gate circuit 98 and waveform 328 shown in Fig. 11 obtained. This Waveform is now applied to control grid 146 of triode 138 in gate circuit 54 and thence to the control grid 132 of pulse selector 56 causing the selection of the 98 kc. pulse 320` coincident with the center of the linear wave. In the present case, the 15,000 ft. pulse is selected and this pulse serves as the triggering pulse 330, Fig. 1l, for the transmitter. The transmitter now transmits a calibration pulse at a time equivalent to an altitude of 15,000 ft. rather than at time zero.

The transmitted calibration pulse normally would cause saturation of the receiver; however relay 332, which it will be remembered is now actuated due to the energization of relay 310, prevents this from occurring. Relay 332 disconnects the receiver from the normal receiving antenna 334 and connects it instead to resistor 336 which now serves as an attenuating means. The transmitted signal therefore is picked up at reduced amplitude by the receiver.

In a preferred form of the invention relay 332 may also be connected to be energized whenever the aircraft is lower than a predetermined altitude such as, for example, 300 to 600 ft. to prevent receiver saturation by a strong echo pulse.

The overall result of circuit operation when calibration switch is closed is that the echo pulse is removed an'd a transmitted calibration pulse occurring at a time equivalent to 15,000 ft. altitude is fed into the receiver (see curve 330, Fig. 11). This calibration pulse is not in proper phase position with respect to steep wave 317 and a D. C. voltage is therefore produced by phase detector 80 of the proper sense again properly to phase the steep wave with the received signal. The motor control circuits will therefore drive the altitude indicator until it indicates about 15,000 ft. at which time the steep Wave will be in the position shown by waveform 338, Fig. 11.

If the indicator does not register precisely 15,000 ft. there is atixed amount of error in the system. Rotating the calibration control 155 which in turn moves arm 209 until the indication is exactly 15,000 ft. will remove this efor. As already explained, rotation of thefcalibration control 155 changes the reference voltage which in turn affects the position of the steep Wave relative to the linear Wave.

Calibration never involves more than a 2500 ft. change in altimeter indication as it operates to the nearest 5000 ft. point any time the equipment is calibrated. An important advantage of this type of calibration is that the calibration error is precisely the same at maximum altitude as at minimum altitude.

An important advantage of the entire system is its extremely high accuracy over its entire range. Accuracy is limited by two factors only, each of which is subject to very close control. One is the degree of matching of the linearity of a potentiometer, which may be controlled very precisely, to the linearity of the linear wave, and the other is the accuracy of an oscillator which also may be controlled precisely. In an embodiment of the invention actually built, the maximum error of the system in fact was found to be fifteen feet. This is a maximum peak error and is not exceeded through .the entire range of the altimeter.

What is claimed is:

l. In a phase shifter, in combination, means producing a first wave having a linear region extending between a first limit and a second limit; means for accurately shifting the phase of said first wave by fixed, known amounts, each not greater than that defined by said region; means for producing a second linear wave having a slope which is substantially greater than that of the linear region of said first wave; means for accurately shifting the phase of said second wave within said region; and means responsive to a shift in phase of said second linear wave with respect to said first linear wave beyond said region in either direction for shifting the phase of said first wave in said direction said known amount.

2. In a phase shifter, in combination, means producing a plurality of pulses spaced in time from one another fixed amounts; means producing a first linear wave extending from one of said pulses beyond an immediately adjacent pulse to at least a third pulse, said wave being linear throughout its entire extent, and having a region extending from a point located approximately midway between said one pulse and said immediately adjacent pulse to a second point approximately mid-way between said immediately adjacent pulse and said third pulse; means for producing a second wave; means for accurately shifting the phase of said second wave with respect to said first wave over said region; and means responsive to a shift in phase of said second wave with respect to said rst wave beyond said region in either direction for shifting the phase of said first Wave in said direction by an angle equivalent to the spacing between adjacent ones of said pulses.

3. A circuit for shifting the phase of a given signal through a predetermined phase angle with respect to a reference signal comprising means for generating timing signals separated in phase from one another given angles which are fractions of said predetermined phase angle, one of said timing signals being in a predetermined phase relationship with said reference signal; means for generating a comparison wave which extends at any instant in a given direction at least from one of said timing signals beyond another of said timing signals adjacent thereto, said Wave including a first portion adjacent said one timing signal and a second portion be-j yond said another timing signal; means for adjusting the phase of said given signal with respect to said comparison Wave over the region of the latters extent between said two portions, said region encompassing a phase angle at least equal to that between two adjacent timing signals; and means responsive to the adjustment of phase of said given signal beyond said region to one 114 of said portions for shifting the phase of said comparison wave one of said given phase angles in the direction of said one portion while maintaining the phase of said given signal with respect to said reference signal the same immediately after said shifting of said comparison wave said given phase angle as immediately before said shifting of said comparison wave said given phase angle.

4. A circuit as set forth in claim 3 wherein siad reference signal comprises a pulse, said comparison wave comprises a linear Wave, and said given signal comprises a linear wave having a Lsubstantially steeper wave front than said comparison wave.

5. A circuit for adjusting the time of occurrence of a first signal relative to a second signal within a given timing range until the former is at a desired time delay with respect to the latter comprising means for generating timing signals spaced from one another known intervals of time which are fractions of said timing range, one of said timing signals being in a given phase relationship with said second signal; means for generating a comparison wave having a .duration greater than the time interval between adjacent pulses and extending from a timing signal beyond at least one adjacent timing signal, said comparison wave having a center region at least equal to the time interval between adjacent pulses and extending from a point adjacent one timing signal to a point beyond said adjacent timing signal, said comparison wave passing through a reference voltage; means for maintaining said first signal at a phase with respect to said comparison wave which is a function of the intersection in point of time of said comparison wave and said reference voltage; means for deriving from said first and second signals a control Voltage having a sense dependent on the sense of the difference in phase between said first and second signals; means responsive to said control voltage for adjusting the direct voltage level of said comparison wave with respect to said reference voltage while maintaining the same phase of said comparison wave with respect to said timing signals; and means responsive to the intersection in point of time of said reference voltage and said comparison Wave beyond said center region of said comparison wave for shifting said comparison wave one of said known intervals of time which is a fraction of said timing range in the direction from the center of said comparison wave toward said last-named intersection in point of time.

6. A circuit as set forth in claim 5 wherein said region of said comparison wave extending from a point adjacent one timing signal to a point beyond said adjacent timing signal is linear.

7. A circuit as set forth in claim 5 wherein said first signal comprises a steep fronted wave and said second signal comprises a pulse.

8. A system operative within a given timing range for continuously indicating a delay interval within said range between a reference signal and a second signal comprising means for generating timing signals spaced from one another predetermined intervals of time which are fractions of said timing range, one of said timing signals being in a predetermined phase relationship with said reference signal; means for generating a first comparison wave in a given phase relationship with another of said timing signals which extends from one limit voltage through a reference voltage to a second limit voltage, said one limit voltage differing in one sense from said reference voltage and said second limit voltage differing in another sense from said reference voltage; means for generating a second comparison Wave at a time determined by the intersection along the time axis of said reference voltage and said first comparison wave; means for comparing the phase of at least a portion of said second comparison wave with that of said second signal and deriving therefrom a control voltage esegesi;

having a sense dependent on they sense of the difference in phase of said second signal from said second cornparison wave from a predetermined phasal relationship; means responsive to said control voltage for adjusting the amplitudes of said limit voltages relative to said reference voltage so as to bring said second comparison wave into said predeterminedy phasal relationship with said second signal while maintaining said first comparison wave in said given phase relationship with said another of said timing signals; and means responsive to a difference in amplitude of less than a predetermined amount between said reference voltage and one of said limit voltages fory shifting said first comparison Wave one f said predetermined fractional intervals of time in the proper sense to render said difference in amplitude between said reference voltage and said one limit voltage greater than said predetermined amount, while maintaining the same intersection point along the time axis of said reference voltage and said first comparison wave,

9. A system operative within a given timing range for continuously indicating a delay interval within said range between a reference signal and a second signal comprising means for generating timing signals spaced from'one another predetermined intervals of time which are fractions of said timing range, one of said timing signals being in a predetermined phase relationship with said reference signal; means for generating a first comparison wave in a given phase relationship with another of said timing signals which extends from one limit voltage through a reference voltage to a second limity voltage, said one limit voltage differing in one sense from said reference voltage and said second limit voltage differing in another. sense from said reference voltage, and which has a duration' substantially greater than the time interval between adjacent ones of said timing signals; means for generating a second comparison wave at a time determined by the intersection along the time axis of said reference voltage and said rst comparison wave; means for comparing the phase of at least a portion of said second comparison wave with. that of said second signal and deriving therefrom a control voltage having a sense dependent on the sense of the difference in phase of said second signal from said second comparison wave from a predetermined phasal relationship; means responsive to said control voltage for adjusting the amplitude of said one of said limit voltages relative to said reference so as to bring said second comparison wave into said predetermined phasal relationship with said another of said timing signals; and means responsive to a difference in amplitude of less than a predetermined amount between said reference voltage and one of said limit voltages for shifting said first comparison wave one of said predetermined fractional intervals of time in the proper sense to render said difference in amplitude between said reference voltage and said one limit voltage greater than said predetermined amount, while maintaining the same the intersection point along the time axis of said reference voltage and said first comparison wave.

10. A system as set forth in claim 9 wherein said timing signals comprise pulses, said comparison wave comprises a linear wave, and said second comparison wave is initiated coincidentally with the point in time that said first comparison wave intersects said reference voltage.

l1. A system operative within a given timing range for continuously indicating a delay interval within said range between a first pulse and a second pulse comprising means for generating timing signals spaced from one another predetermined intervals of time which are fractions of said timing range, one of said timing signals being in phase with said first pulse; means for generating a first linear wave in phase with a timing signal which extends from one limit voltage through a reference voltage to a second limit voltage, said first linear wave extending from one timing signal beyond at least one other timing signalrand having a center region having a duration at least equal to the time interval between timing signals; means for generating a second linear waver at a time determined by the intersection along the time axis of said reference voltage and said first linear wave, said second linear wave having a substantially steeper slope than said first linear wave; means for comparing the phase of atleast a portion of said second linear wave with that of said second pulse and deriving therefrom a control voltage having a sense dependent on the sense of the difference in phase of said second pulse from said second linear wave; means responsive to said control voltage for adjusting the amplitude of'said limit voltages relative to said reference voltage so as to bring said second linear wave into phase with said second pulse'while maintaining said first linear wave in the same phase relationship with said timing signals;l and means responsive tothe intersection along the time axis of said reference voltage and said first linear wave at a point outside of said center region of saidrst linear wave `for shifting said first linear wave yone of said predetermined fractional intervals of ,time in the proper sense to return the point of intersection of said reference voltage and said firstflinear wave to said center region of said first linear wave, while maintaining the same the intersectiony point along the time axis of said first linear wave and said reference voltage.

12. A system as set forth in claim l1 and further including means including a mechanical indicating device responsive to said control voltage for continuously indicating the delay interval between said first pulse and said secondy pulse. y

13. In a pulse-echo system including transmitter means for transmitting a pulse to a reflecting object and receiver means forfreceiving an echo pulse from said object, in combination, means for generating timing pulsesy spaced from one another predetermined intervals of time which are fractions of the time required for said transmitted pulse to reach the furthest object of interest and be reflected therefrom; synchronizing means for synchronizing the phase of one of said timing pulses with that of said transmitted pulse; means for generating a first linear wave in phase with a timing pulse which extends from one limit voltage through a reference voltage to a second limit voltage, said first linear wave extending from one timing pulse beyond at least one other timing pulse and having a center region having a duration at least equal to the time interval between timing pulses, said echo pulse occurring at a time within the time of occurrence of said center region; means for generating a second linear wave at a time determined by the intersection along the time axis of said reference voltage and said first linear Wave, said second linear wave having a substantially steeper slope than said first linear wave; means for comparing the phase of at least a portion of said second linear wave with that of said echo pulse and deriving therefrom a control voltage having a sense dependent on the sense of the difference in phase between said echo pulse and said second linear wave; means responsive to said control voltage for adjusting the direct voltage level of said first linear wave so as to bring said second linear wave into phase with said echo pulse while maintaining said first linear wave in the same phase relationship with said timing pulses; and phase shifting means responsive to the intersection along the time axis of said reference voltage and said first linear wave at a point outside of said center region of said first linear wave for shifting said first linear wave one of said predetermined fractional intervals of time in the proper sense to return the point of intersection of said reference voltage and said first linear wave to said center region of said first linear wave, while maintaining the same the intersection point along the time axis of said first linear wave and said reference voltage. t

14. A pulseeecho system as set forth in claim 13 wherein said phase shifting means includes a plurality of binary divider stages connected in cascade for generating a gate signal having a phase dependent on the manner of connection of the outputs of the individual ones of said stages; and selector means responsive to said control voltage for selecting the desired combination of outputs of said individual stages.

15. A pulse-echo system as set forth in claim 14 and further including direct reading indicator means for indicating the distance of an object from which a transmitted pulse is reliected as an echo pulse; and indicator control means responsive to said control voltage for actuating said indicator.

16. A pulse-echo system as set forth in claim 13 and further including a calibration system comprising means for blocking said receiver during the normal period of reception of said echo pulse; and means for actuating said transmitter causing it to transmit a calibration pulse incoincidence with the timing pulse closest in point of time tosaid echo pulse, whereby said pulse-echo system should indicate a distance equivalent to the time delay between the normal transmitted pulse and said calibration pulse.

17. A pulse-echo system as set forth in claim 16 and further including attenuating means in said receiver for attenuating said calibration pulse to prevent the latter from driving the receiver to saturation.

18. A pulse-echo system as set forth in claim 13 and further including indicating means responsive to said control voltage for indicating the distance of said object reecting said echo pulse; and a calibration system comprising means for blocking said receiver during the normal period of reception of said echo pulse; and means for actuating said transmitter causing it to transmit a calibration pulse in coincidence with the timing pulse closest in point of time to said echo pulse, whereby said pulseecho system should indicate on said indicating means a distance equivalent to the time delay between the normal transmited pulse and said calibration pulse.

19. A pulse-echo system as set forth in claim 18 and further including means for adjusting said reference voltage to correct any inaccuracies in the distance indication provided by said indicator during calibration thereof.

20. A pulse-echo system as set forth in claim `l and further including a calibration system comprising means for blocking said receiver during the normal period of reception of said echo pulse; and means for' actuating said transmitter causing it to transmit a calibration pulse in coincidence with the timing pulse closest in point of time to said echo pulse, whereby said pulse-echo system should indicate a distance equivalent to the time delay between the normal transmitted pulse and said calibration pulse.

2l. In a phase shifter, in combination, means producing a first wave having a linear region extending between a first limit and a second limit; means for accurately shifting the phase of said first wave by Xed, known amounts, each not greater than that defined by said region, over a given phase angle; means for producing a reference voltage; means responsive to a predetermined amplitude relationship between said first linear wave and said reference voltage for producing a second wave; means including a source of clamping voltage for adjusting the direct potential level of said rst wave for smoothly shifting the phase of said second wave within said region; and means responsive to a shift in phase of said second wave with respect to said rst wave beyond said region in either direction for shifting the phase of said reference wave in that direction said known amount and simultaneously adjusting the level of said clamping voltage to a point such that said shift in phase of said first wave has no eect on said second wave.

22. In a phase shifter, in combination, means producing a reference voltage; means producing a first wave having a linear region extending between a iirst limit and a second limit, and passing through said reference voltage; means for accurately shifting the phase of said first wave by lixed, known amounts, each not greater than that deiined by said region over a given phase angle; means responsive to the intersection in point of time of said rst wave with said reference voltage for producing a second wave; clamping means including a source of clamping voltage for adjusting the direct potential level of said first wave for smoothly shifting the phase of said second wave within said region; and phase shifting means responsive to a shift in phase of said second wave with respect to said irst wave beyond said region in either direction for shifting the phase of said first wave in that direction said known amount and simultaneously adjusting the level of said clamping voltage to a new value such that the intersection in point of time of said rst wave with said reference Wave is substantially the same after the shift thereof as before the shift thereof.

23. In a phase shifter as set forth in claim 22, said clamping means including a linear potentiometer.

24. In a phase shifter as set forth in claim 22, said clamping means including a linear potentiometer having a pair of arms, one of said arms being in circuit at a time, said arm in circuit providing an adjustable level of clamping voltage; and further including arm selector means responsive to said shift in phase of said second Wave with respect to said first wave beyond said region for removing said arm in circuit and placing the other of said arms n circuit with said linear potentiometer to select a new level of clamping votage such that the shift in phase of said first wave said known amount has no effect on the phase of said second wave.

25. In a phase shifter as set forth in claim 24, said phase shifting means including a plurality of binary divider stages connected in cascade for generating a gate signal having a phase dependent on the manner of connection of the outputs of the individual ones 'of said stages; and selector means responsive to the shift in phase of said second wave with respect to said first wave beyond said region for selecting the desired combination of outputs of said individual stages.

26. In combination, means for generating a reference wave; means for generating a second Wave; means for measuring the phase of said second wave with respect to said reference wave within predetermined angular limits; and means responsive to the phase difference between said waves at either one of said limits for shifting the phase of said reference wave by a given known amount, not greater than the phase angle defined by said two limits, in the direction of said one limit.

27. In combination, means for generating a reference wave; means for generating a second wave; means for measuring the phase of said second wave with respect to said reference Wave within predetermined angular limits; and means responsive to the phase difference between said waves at one of said limits for shifting the phase of said reference wave by a given known amount equal to the phase angle defined by said two limits, in the direction of said one limit.

28. In combination, means for generating a reference wave; means for generating a second wave; means for measuring the phase of said second wave with respect to said reference wave within predetermined limits; and means responsive to the phase difference between said waves Whenever said second wave reaches either one of said limits for shifting the phase of said reference wave by an amount equal to the phase angle defined by said two limits, in the direction of said one limit.

29. In combination, means for generating -a first linear wave; means for generating a second linear wave having a slope substantially steeper than that of said first linear Wave; means for measuring the phase of said second linear wave with respect to said rst linear wave within predetermined limits; and means responsive to the phase 19 20 difference between said waves whenever said second linear References Cited in the le of this patent wave attains either one of said limits for shifting the UNITED STATES PATENTS phase of said rst linear wave by a given known amount u t A equal to the phase angle defined by said two limits, in 2513988 `W01ff July 4 1950 5 FOREIGN PATENTS A the direction of said limit.

522,072 Great Britain Mar. 22, 1945`

Images